Emails Stopped. What do I do?

Resolving delivery failures to your email address

Updated over a week ago

Since our software delivers thousands of emails daily, email systems can occasionally block or reject emails from our system. If you're receiving the message shown above, then our system successfully attempted to deliver an email to your email address, but your email server rejected the message and sent it back to us. This can happen for several reasons, but some of the most common are:

  • The email address no longer exists.

  • The email address is misspelled.

  • The email box is full.

  • The email server thinks our message is spam.

  • The recipient (or the recipient's school or company) blacklisted our emails.

  • The recipient's mail server suffers (or did suffer) from a temporary outage.

Unfortunately, there isn't anything we can do to resolve this issue. The fact that you received this message shows that our systems are working normally, but the receiving server explicitly rejected or refused to accept the message. The recipient (you) will need to resolve this with your email provider. Here's what you can do to resolve the issue on your end:

  1. Click the "Find Out Why" button to see exactly why the email was rejected. The "Find Out Why" window will show you the exact, uncensored response that the receiving email server sent back to our systems which the recipient's email provider can use to resolve the issue and pinpoint the exact cause of the rejection.

  2. Contact your email provider and give them the exact message from the "Find Out Why" window.

  3. Ask your email provider to whitelist our sending domains. You'll need to whitelist all of the following domains:,,

  4. Ask your email provider to whitelist our sending addresses. All emails from our system come from one of the following addresses:

  5. Email providers are less likely to mark items as spam if the email address is in your Contacts list. Consider adding Horizon as one of your contacts with the email addresses listed in Step #5 above. Be sure this contact is labeled as Horizon to avoid the Local Contacts Override problem.

  6. If you're sure the issue is resolved, you can dismiss the notifications from the Reminders box on the Members Home page, allowing email sending to resume to your email address.

  7. If the reminder continues to come back after dismissing it, the issue is still unresolved, and you'll need to contact your email provider further.

  8. If you use Network Solutions as your email provider, you can see this support article for specific instructions for that provider.

  9. If you use a email address, you can see this support article for specific instructions for that provider.

  10. You can use an alternative email address if you still can't resolve the issue. We recommend Gmail.

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